1. Field of the Invention.
The invention relates generally to the art of railway signalling and communication. More particularly, the invention relates to an apparatus and method utilizing fiber optic sensing to detect the presence of a railway vehicle within a track section as well as other conditions and parameters.
2. Description of the Prior Art.
Typical wayside instrumentation systems for railway and transit installations interconnect the central office to wayside equipment such as switch and signal devices so that traffic flow may be remotely directed. To prevent the establishment of conflicting routes, such instrumentation systems incorporate logical operation to disallow improper commands from the central office or other wayside equipment. This requires that the system have the capability of detecting the presence of railway vehicles within the controlled territory.
This train detection capability is typically provided by the railway track circuit. Generally, railway track circuits detect the presence of a railway vehicle by electrical alteration of a circuit formed by the rails and the vehicle wheel and axle sets. While there are many variations, such track circuits are typically connected within fixed-location, fixed-length sections of a track route known as blocks. Blocks may range in length from hundreds of feet to a maximum of approximately two to five miles.
To minimize the installation and maintenance of wayside communication, some railway track circuits have been employed which send control data between wayside locations using unoccupied blocks as a transmission medium. These track circuits are referred to as "coded track circuits." Once a vehicle enters a block having a coded track circuit, the communication link to the next wayside location is severed, but that unit then positively detects the presence of the vehicle. The track circuit codes, as well as the break in continual communication, are important input data to all wayside locations for control operations.
Alternative train operation systems have recently been proposed which require more accurate train detection than may be provided by present track circuits. One such system is the Advanced Train Control System ("ATCS") of the Association of American Railroads. For ATCS, and other proposed "moving block" or minimal headway systems, location resolution on the order of one meter may be important for effective control. Current railway systems could also benefit from this degree of resolution to permit vehicles to operate closer together and with a higher level of accuracy.
Additionally, track circuits employed in mainline areas also generally lack the capability to determine direction of motion, count axles or cars, communicate at rates higher than 100 bits per second, or determine the presence and location of fire in a tunnel.